How many microstates are defined to exist at absolute zero for a perfect crystal?
The third law of thermodynamics states that in that case, the absolute entropy becomes zero for a perfect crystal:
#S = 0#at #T = "0 K"#.
Statistically, from Boltzmann's theorem,
#S = 0 implies ln W = 0#
#W#is the number of microstates occupied.
However, quantum fluctuations make it difficult that such a state becomes localised because the fluctuations occurring are non-negligible compared to the energy available.
This has an important implication - absolute zero is difficult to maintain.